This invention relates to curable composite direct filling materials for dental restoration. More particularly, it relates to compositions containing an organic filler.
Direct filling materials are compositions useful for repairing damaged teeth in situ. Direct filling materials containing curable acrylic binder resins such as methyl methacrylate, the reaction product of bisphenol A with glycidal methacrylate, and other resins containing acrylic functionality together with suitable catalysts such as peroxides, hydroperoxides, and photoinitiators (e.g. benzoin ethers) have been widely used for repairing teeth due to their realistic appearance and ease of preparation and use, see "Dental Applications," Encyclopedia of Polymer Science and Technology, 4, 727 (Wiley, 1966). In addition, such resins have also been used to manufacture artificial teeth and denture bases, id at 728, 733. Unfilled (i.e., pure) curable acrylic binder resins generally suffer from polymerization shrinkage and poor durability. These drawbacks have been reduced in direct filling applications, in part, through the addition of inert fillers (see U.S. Pat. No. 3,066,112). The combination of binder plus filler is commonly referred to as a composite direct filling material. Currently used fillers for curable acrylic binder resins generally are inert inorganic materials in the form of finely divided irregular particles, fibers or beads, present in from about 35 to about 80 percent by weight of the total composite direct filling material. Many publications have stressed that suitable filler materials should have low coefficient of thermal expansion, high compressive strength, and high Rockwell Hardness in order to prevent loosening of the cured direct filling material, increase wear resistance, and reduce polymerization shrinkage, see U.S. Pat. Nos. 3,066,112, and 3,503,128, "Dental Applications" id at 734-736, and Lee, Orlowski, and Kobashigawa, Handbook of Dental Restoratives (1973) pg. 2.20-2.21.
Commonly used inorganic fillers include fused silica, quartz, glass, various mineral silicates (e.g. .beta.-eucryptite, lepidolite, petalite, spodumene, beryl, topaz and zircon), silicon carbide, and alumina. In general, composite direct filling materials which are fully loaded with inorganic fillers (i.e. combined with the highest workable volume loading) are the most wear-resistant currently available composite direct filling materials. However, composite direct filling materials containing finely divided inorganic fillers and acrylic binder resins do not polish as easily as unfilled acrylic binder resin.
U.S. Pat. No. 3,923,740 describes a composite direct filling material containing finely divided cured polymethyl methacrylate as a filler, alone or in conjunction with an inorganic filler. Composite direct filling materials which are wholly or partly filled with finely divided polymethyl methacrylate have better polishability (i.e. better surface finish after polishing with ordinary dental tools) than composite direct filling materials which are fully loaded with inorganic fillers, but generally have poorer durability (i.e. poorer wear resistance in vivo) than such fully inorganically filled composite direct filling materials.
It is an object of the present invention to provide a composite direct filling material with an abrasion resistant, resilient surface that has greater durability than composite direct filling materials (that are fully loaded with inorganic materials) while providing good polishability. It is an additional object of the present invention to provide a composite direct filling material with low polymerization shrinkage and low solubility in mouth fluids. It is an additional object of the present invention to provide a dental restorative material useful for the manufacture of replacement teeth or denture bases. Further objects and advantages of the present invention will become apparent from the following description of the invention.